A silicon compound is an important and indispensable material in the semiconductor field. For example, a silicon oxide film is used as a gate insulating film of a semiconductor element, and an amorphous silicon film, a silicon nitride film or the like is used as a thin film transistor of a semiconductor element. In addition, a polycrystalline silicon material is used for a three-dimensional structural element such as an MEMS or the like, and silicon carbide (SiC) is used for a low power consumption transistor or the like. In this manner, a silicon compound is used widely. Especially, a semiconductor element such as a transistor or the like included in a DRAM or a flash memory is highly integrated progressively, and thus a silicon semiconductor device is a target of attention.
Usually in a semiconductor production process, silicon or a silicon compound is processed into a predetermined shape or removed in a predetermined step such as a final step or the like. For processing or removing a silicon compound in this manner, dry etching is conventionally used widely.
The present inventors found that use of iodine heptafluoride for an etching material realized selective etching of silicon (see Japanese Laid-Open Patent Publication No. 2014-150169). However, in the case where this technique is used for etching in the state where moisture is contained in a chamber or a gas discharge pipe, an iodine oxide represented by chemical formula IxOyFz (x represents an integer of 1 or 2, y represents an integer of 1 or greater and 5 or less, and z represents an integer of 0 or 1) may be generated by the following reaction and attached to the inside of the chamber or a wall of the gas discharge pipe.IF7+nH2O→IxOyFz+HF  Reaction expression:
The reaction for etching a silicon thin film on a substrate by use of iodine heptafluoride is represented by the following expression.Si+2IF7→SiF4+2IF5 
At the time of etching, a by-product or an iodine compound such as iodine pentafluoride (IF5) or the like may be attached to the inside of the chamber or the wall of the gas discharge pipe, or deposited on a surface of the substrate, by decomposition of etching gas.
When a substrate such as an Si wafer or the like is introduced into the chamber in the state where an iodine oxide or an iodine compound (hereinafter, an iodine oxide and an iodine compound may be collectively referred to as a “iodine-containing substance”) is attached to the inside of the chamber or the wall of the gas discharge pipe, the iodine-containing substance that is volatized when the inside of the chamber is made vacuum and the internal atmosphere of the chamber is replaced with an inert gas is attached to the substrate such as the Si wafer or the like. There is a problem that an inconvenience such that, for example, the etching rate is decreased or the etching does not proceed properly by the influence of the iodine-containing substance attached to the substrate.
If the iodine compound generated at the time of etching is kept deposited to the surface of the substrate, the surface of the substrate is kept contaminated with iodine. If the surface of the substrate is exposed to the air in this state, the iodine compound reacts with moisture in the air to generate hydrogen iodide (HI), iodic acid (HIO3) or the like. This causes a problem of possibly inducing corrosion of a metal component in the chamber, the gas discharge pipe or the like.
Japanese Laid-Open Patent Publication No. 2013-46001 discloses the following etching method using iodine heptafluoride. A reactive gas (interhalogen compound or hydrogen fluoride) and an inert gas are mixed together and jetted into the chamber while a gas supply path to the chamber is cooled and heat-insulated to be expanded. Thus, reactive clusters are generated in the chamber and used to perform etching and cleaning. The method of Japanese Laid-Open Patent Publication No. 2013-46001 puts the reactive gas into clusters to increase the etching rate.
Japanese Laid-Open Patent Publication No. 2013-46001 describes the interhalogen gas and HF as the reactive gas, and describes iodine heptafluoride as an example of such a reactive gas. However, Japanese Laid-Open Patent Publication No. 2013-46001 does not describe any iodine-containing substance generated as a by-product or does not disclose any influence of the iodine-containing substance on etching. With the technique of Japanese Laid-Open Patent Publication No. 2013-46001, an iodine oxide is generated by the influence of the moisture in the chamber or the gas discharge pipe. Therefore, the inconvenience regarding etching is not suppressed, and the object of suppressing the inconvenience caused at the time etching and improving the productivity is not achieved.
Japanese Laid-Open Patent Publication No. 2011-208193 discloses a method of cleaning a vacuum gas discharge pipe, more specifically, a method of using an interhalogen compound to clean a suction pipe related to a semiconductor film production device and a vacuum pump. Japanese Laid-Open Patent Publication No. 2011-208193 describes iodine heptafluoride as a reactive gas. However, Japanese Laid-Open Patent Publication No. 2011-208193 does not describe any iodine-containing substance generated as a by-product or does not disclose any influence of the iodine-containing substance on etching. In Japanese Laid-Open Patent Publication No. 2011-208193, a deposited film of amorphous silicon, silicon dioxide or a dopant is removed by cleaning, but an iodine-containing substance derived from a reactive gas is not described.
Japanese Patent No. 4999400 discloses the following method for dry-etching an oxide semiconductor film. An oxide semiconductor film containing In, Ga and Zn is etched by use of Cl2 or Cl2/Ar under the following conditions (chamber pressure: 0.06 Pa or greater and 5 Pa or less; and density of the bias RF power applied to the substrate side: 0.02 W/cm2 or greater). It is described that this method suppresses the end of a pattern of the vapor-deposited film from being turned up when the photoresist is removed and thus improves the yield as compared with a conventional lift-off method. However, the film to be removed by the method of Japanese Patent No. 4999400 is an oxide semiconductor film containing In, Ga and Zn, and Japanese Patent No. 4999400 does not describe removal of an iodine-containing substance. In addition, if an iodine-containing substance is removed under the conditions of Japanese Patent No. 4999400, an Al-based material, which is a component of an etching device, is corroded. This is not preferable.
As described above, there is no document that describes generation of an iodine oxide caused by moisture in a chamber or a gas discharge pipe, and the problem that the generation of an iodine oxide causes an inconvenience regarding etching and decreases the productivity is not known. Currently, no measure is known against the inconvenience regarding etching that is caused by an iodine-containing substance encompassing an iodine oxide and also an iodine compound generated at the time of etching. There is a problem that the chamber needs to be disassembled and cleaned in order to remove such an iodine-containing substance.
The present invention made in light of the above-described problems has an object of suppressing an inconvenience at the time of etching performed by use of an etching gas containing iodine heptafluoride or the like.